title: Hypoxia-induced inhibition of epithelial Na(+) channels in the lung. Role of Nedd4-2 and the ubiquitin-proteasome pathway.
abstract: Transepithelial sodium transport via alveolar epithelial Na(+) channels (ENaC) and Na(+),K(+)-ATPase constitutes the driving force for removal of alveolar edema fluid. Alveolar hypoxia associated with pulmonary edema may impair ENaC activity and alveolar Na(+) absorption through a decrease of ENaC subunit expression at the apical membrane of alveolar epithelial cells (AECs). Here, we investigated the mechanism(s) involved in this process in vivo in the β-Liddle mouse strain mice carrying a truncation of β-ENaC C-terminus abolishing the interaction between β-ENaC and the ubiquitin protein-ligase Nedd4-2 that targets the channel for endocytosis and degradation and in vitro in rat AECs. Hypoxia (8% O2 for 24 h) reduced amiloride-sensitive alveolar fluid clearance by 69% in wild-type mice but had no effect in homozygous mutated β-Liddle littermates. In vitro, acute exposure of AECs to hypoxia (0.5-3% O2 for 1-6 h) rapidly decreased transepithelial Na(+) transport as assessed by equivalent short-circuit current Ieq and the amiloride-sensitive component of Na(+) current across the apical membrane, reflecting ENaC activity. Hypoxia induced a decrease of ENaC subunit expression in the apical membrane of AECs with no change in intracellular expression and induced a 2-fold increase in α-ENaC polyubiquitination. Hypoxic inhibition of amiloride-sensitive Ieq was fully prevented by preincubation with the proteasome inhibitors MG132 and lactacystin or with the antioxidant N-acetyl-cysteine. Our data strongly suggest that Nedd4-2-mediated ubiquitination of ENaC leading to endocytosis and degradation of apical Na(+) channels is a key feature of hypoxia-induced inhibition of transepithelial alveolar Na(+) transport.
authors.affiliation: 1 Université Paris 13, Sorbonne Paris Cité, Laboratoire Réponses Cellulaires et Fonctionnelles à l'Hypoxie (EA 2363), Bobigny, France.
authors.forename: Thomas
authors.initials: T
authors.lastname: Gille
authors.forename: Nadia
authors.initials: N
authors.lastname: Randrianarison-Pellan
authors.forename: Arnaud
authors.initials: A
authors.lastname: Goolaerts
authors.forename: Nicolas
authors.initials: N
authors.lastname: Dard
authors.forename: Yurdagül
authors.initials: Y
authors.lastname: Uzunhan
authors.forename: Evelyne
authors.initials: E
authors.lastname: Ferrary
authors.forename: Edith
authors.initials: E
authors.lastname: Hummler
authors.forename: Christine
authors.initials: C
authors.lastname: Clerici
authors.forename: Carole
authors.initials: C
authors.lastname: Planès
mesh_terms: D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D015687:Cell Hypoxia; D002478:Cells, Cultured; D004195:Disease Models, Animal; D004705:Endocytosis; D056827:Endosomal Sorting Complexes Required for Transport / Q000378:metabolism*; D004847:Epithelial Cells / Q000187:drug effects / Q000201:enzymology*; D053503:Epithelial Sodium Channels / Q000172:deficiency / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D000860:Hypoxia / Q000201:enzymology* / Q000235:genetics; D008297:Male; D008564:Membrane Potentials; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009079:Mucociliary Clearance; D000075702:Nedd4 Ubiquitin Protein Ligases; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D061988:Proteasome Inhibitors / Q000494:pharmacology; D011650:Pulmonary Alveoli / Q000187:drug effects / Q000201:enzymology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000378:metabolism*; D026941:Sodium Channel Blockers / Q000494:pharmacology; D013997:Time Factors; D025801:Ubiquitin / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*
chemical_list: D000975:Antioxidants; D056827:Endosomal Sorting Complexes Required for Transport; D053503:Epithelial Sodium Channels; D061988:Proteasome Inhibitors; C507047:Scnn1a protein, mouse; C440894:Scnn1a protein, rat; C507049:Scnn1b protein, mouse; C507050:Scnn1b protein, rat; C507053:Scnn1g protein, mouse; C507054:Scnn1g protein, rat; D026941:Sodium Channel Blockers; D025801:Ubiquitin; D012964:Sodium; C000618479:NEDD4L protein, rat; D000075702:Nedd4 Ubiquitin Protein Ligases; C000618484:Nedd4 protein, rat; C000618461:Nedd4l protein, mouse; D044767:Ubiquitin-Protein Ligases; D046988:Proteasome Endopeptidase Complex